CO2 Lags Temperature in the Ice-Core Record. Doesn’t that prove the IPCC wrong?

I’m halfway through writing the 2nd post in the series CO2 – An Insignificant Trace Gas? – which is harder work than I expected and I came across a new video by John Coleman called Global Warming: The Other Side.

I only watched the first section which is 11 minutes long and promises in its writeup:

..we present the rebuttal to the bad science behind the global warming frenzy.. We show how that theory has failed to verify and has proven to be wrong.

The 1st video section claims to show the IPCC wrong but is actually a critique of one section of Al Gore’s movie, An Inconvenient Truth.

The presenter points out the well-known fact that in the ice-core record of the last million years CO2 increases lag temperature increases. And this appears to be the complete rebuttal of “CO2 causes temperature to increase”.

The IPCC has a whole chapter on the CO2 cycle in its TAR (Third Assessment Report) of 2001.

A short extract from chapter 3, page 203:

..Whatever the mechanisms involved, lags of up to 2,000 to 4,000 years in the drawdown of CO2 at the start of glacial periods suggests that the low CO2 concentrations during glacial periods amplify the climate change but do not initiate glaciations (Lorius and Oeschger, 1994; Fischer et al., 1999). Once established, the low CO2 concentration is likely to have enhanced global cooling (Hewitt and Mitchell, 1997)..

So the creator of this “documentary” hasn’t even bothered to check the IPCC report. They agree with him. And even more amazing, they put it in print!

If you are surprised by either of these points:

CO2 lags temperature changes in the last million years of temperature history

The Oceans Store CO2

“All other things being equal”, as the temperature of the oceans rises, CO2 is “out-gassed” – released into the atmosphere. As the temperature falls, more CO2 is dissolved in.

“All other things being equal” is the science way of conveying that the whole picture is very complex but if we concentrate on just two variables we can understand the relationship.

“All Other Things being Equal”

Just a note for those interested..

In the current environment, we (people) are increasing the amount of CO2 in the atmosphere. So, currently as ocean temperatures rise CO2 is not leaving the oceans, but in fact a proportion of the human-emitted CO2 (from power stations, cars, etc) is actually being dissolved into the ocean.

So in this instance temperature rises don’t cause the oceans to give up some of their CO2 because “all other things are not equal”.

Doesn’t the fact that CO2 lags temperature in the ice core record prove it doesn’t cause temperature changes?

It does prove that CO2 didn’t initiate those changes of direction in temperature. In fact the whole subject of why the climate has changed so much in the past is very complex and poorly understood, but let’s stay on topic.

Let’s suppose that there is an increase in solar radiation and so global temperatures increase. As a result the oceans will “out gas” CO2. We will see a record of CO2 changes following temperature changes.

But note that it tells us nothing about whether or not CO2 itself can increase temperatures.

[It might say something important about Al Gore’s movie.]

More than one factor affects temperature rise. There are lots of inter-related effects in the climate and the physics and chemistry of climate science are very complex.

Conclusion

Whether or not the IPCC is correct in its assessment that doubling CO2 in the atmosphere will lead to dire consequences from high temperature rises is not the subject of this post.

This post is about a subject that causes a lot of confusion.

I haven’t watched Al Gore’s movie but it appears he links past temperature rises with CO2 changes to demonstrate that CO2 increases are a clear and present danger. He relies on the ignorance of his audience. Or demonstrates his own.

“Skeptics” now arrive and claim to “debunk” the science of the IPCC by debunking Al Gore’s movie. They rely on the ignorance of their audience. Or demonstrate their own.

CO2 is certainly very important in our atmosphere despite being a “trace gas”. Physics and the properties of “trace gases” cannot be deduced from our life experiences. Have a read of CO2 – An Insignificant Trace Gas? Part Oneto understand more about this subject.

CO2 is both a cause and a consequence of temperature changes. That’s what makes climate science so fascinating.

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33 Responses

Has the amount of CO2 released from the oceans in response to a 1 degree C temperature rise (“All other things being equal”) been calculated? How does that compare to what we have seen in the last 150 years?

I think you may be missing the point. While the IPCC addresses the lag in CO2 decrease at the start of a glaciation period, the more damning evidence is the lag in CO2 increase at the start of a warmer period — proving that temperature increases can happen quite naturally without being invoked by increases in CO2.

“High-resolution records from Antarctic ice cores show that carbon dioxide concentrations increased by 80 to 100 parts per million by volume 600 ± 400 years after the warming of the last three deglaciations.”

Possibly, but I don’t know the answer. I’m sure someone has done some lab experiments as well but the subject in practice is very tricky. You could take a sample of the ocean and try it out but each experiment would depend on salinity, ocean temperature and the precise chemistry of that sample. As you go deeper the pressure changes and that also affects solubility of CO2.

I would also like to see the range of possible values for some representative ocean samples.

Note that the increase in CO2 in the atmosphere is not from the oceans. How do we know? Because of the isotope ratio.

There is one more factor involved in the ‘CO2-ocean-outgassing’ situation which you did not mention, but which is extremely influential….

Phytoplankton.

In particular, the growth of phytoplankton in response to increased availability of food (CO2) dissolved in the water (and,perhaps, further aided by the increase in solar radiation energy…). As the phytoplankton gobbles up the CO2, converting it into food for all the marine creatures higher up the food chain, it reduces the levels of CO2 dissolved in the ocean – and thus reduces the amount of CO2 available for ‘out-gassing’….

Photos of the planet over the last 5-7 years demonstrate a significant increase in phytoplankton, especially in temperate regions of the oceans. The pictures are green now, where they used to be blue….

This is not often addressed adequately in the scientific analysis – well, most of them – which use a straight mathematical relationship…this much dissolved therefore this much will be available for out-gassing.

Except that it isn’t.

It has entered the food chain instead.

Of course, I do not know the answers – I don’t think anyone has sufficient grasp of all the factors involved to have any definitive answers. Just that, hardly anyone ever mentions the increased growth of phytoplankton – and it IS a significant factor.

You are right about phytoplankton. The rate at which the net removal of CO2 can proceed due to phytoplankton is limited by the availability of other nutrients in the top 200m of the ocean – as there is plenty of CO2 and solar energy for them.

The nutrients get depleted in the surface layer but are abundant lower down. So when there is upwelling of deeper ocean water the phytoplankton can increase their removal of CO2.

One finding was that the rate of exchange of CO2 between ocean and atmosphere in the mid-latitude Pacific varies from year to year by as much as a factor of 4.

You completely missed the point. Many scientists use this Vostok record to calculate CO2 sensitivities yet they really can’t say with any certainty what the proportion of amplification was: Severinghaus et al. suggested 30% but it’s a pure and utter guess. There is nothing in the physics that argues that the amplification can’t be negligible. Lowell Stotts empirical data indeed suggests it is negligible. Also nobody attempts to explain how this very weak trigger is supposed to overcome these powerful GHG feedbacks in order to restart the cooling period. For that you need a sudden carbon sink or a sudden cooling amplifier cutting in. Imagine it as a sudden removal of the blanket or the heater in the room being switched off. If it was all about temperature dependent heating amplifiers then the sharpness of the changes would be missing and the cooling would be more gradual. The Vostok record shows utter linearity of CO2 with temperature so it can’t be therefore a cooling amplifier – we need therefore a sudden carbon sink.

I’ve long asked people where is this large sink and i eventually discovered that the only argument that deals with the onset of cooling was Alley’s idea of rock weathering which also increases as the temperature gets warmer. Thus he gave CO2 the title of thermostat. I’ve a feeling this sits uneasily with most scientists, since they don’t talk about it much. Certainly I don’t see how that is any more than a handwave that fails to explain the extreme sharpness of the changes nor do i understand why CO2 should fill the role of Earths thermostat when H2O seems a far better candidate, and indeed is usually described as such in textbooks. ie If we say that H2O (polar ice albedo, clouds, tropical water vapour, ocean cycling) is both the heating and cooling amplifier then we don’t actually need to invoke CO2 at all. CO2 is only then a mere unimportant follower which may have been just put on a pedestal because of more political considerations, ie that it is produced by these big oil companies that are inherently despised by many earth scientists. I say that because in the 70’s there was an effort to blame cooling on fossil fuels too which seems like institutionalized bias to me.

I wonder something else too that nobody seems to think about. Suppose the sharp changes in the Vostok record simply happened because of a regular shift in wind direction thanks to regular magnetic or orbital shifts. We know that can happen but it’s not even considered. This is the big problem with extending one data proxy in one location on earth and extrapolating over the entire globe. Where’s the other evidence – well we have stomata proxies that actively contradict the theory. Well we can’t have that inconvenience to our simplistic one-size-fits-all theory so let’s just cast doubt on those conflicting proxies shall we? Now do you see the point?

You wrote –
“CO2 is both a cause and a consequence of temperature changes” and those who disagree with the causation part “rely on the ignorance of their audience. Or demonstrate their own”. Your words!

Yet neither Coleman, his scientific advisors, nor his audience are unaware of the realclimate.org inspired arm-waving argument that CO2, while clearly not a driver, might have been an important heating amplifier during the heating part of the ice-age cycles. It’s only a point of view though, and one that the data doesn’t actually suggest by itself, despite folk like Gore and Hansen trying to tell us otherwise.

The failure of the argument lies in realizing the blindingly obvious fact that it is only in actuality half an argument because you need a cooling mechanism for the other half of the cycle and that is very rarely defined (it took me long enough to discover the iffy rock-weathering argument). Instead Gore’s audience are given the impression that a follower heating amplifier magically switches into a follower cooling amplifier when it’s atmospheric concentration is at a maximum. Now while H20 CAN be a cooling amplifier via cloud formation, CO2 simply cannot unless a massive and sudden CO2 sink just happens out of the blue. This is the step 2 – “then a miracle happens” – part of the hypothesis which surely no scientist can be unaware of. Hence the promotion of this unscientific half-argument into an irrefutable causative effect by Gore and the scientists who advise him and defend him is utterly dishonest. Coleman understands that and his audience understand it. Perhaps only you don’t.

Perhaps you have read into my post more than I claimed. I think it’s important to move step at a time, rather than bite off “the complete theory of all climate change” in one post.

You said (comment Feb 1st):

You completely missed the point. Many scientists use this Vostok record to calculate CO2 sensitivities yet they really can’t say with any certainty what the proportion of amplification was: Severinghaus et al. suggested 30% but it’s a pure and utter guess…

I made no claim about CO2 sensitivities. From my post (what I actually wrote), CO2 could have a minor or insignificant role in amplification of temperature movements that began from other causes, or completely explain everything about climate. I made no claim, so it is a mistake to assume.

I did point out that the IPCC agreed with Coleman that CO2 lags past temperature rises. This was the major point of the post.

And a part that so many get confused by. CO2 lagging temperature in the past doesn’t mean that it can’t influence temperature now.

And on to your next comment (Feb 3rd):

You wrote: “CO2 is both a cause and a consequence of temperature changes” and those who disagree with the causation part “rely on the ignorance of their audience. Or demonstrate their own”. Your words!..

You have re-arranged what I said, and inserted an editorial point I didn’t make. So in fact, I could just say, “Go and reread what I wrote because that isn’t it!”

But instead, in the cause of everyone getting along..

Your first quote “CO2 is both a cause and a consequence of temperature changes” is my final summing up.

The second “quote” is a misrepresentation of what I said.

What did I say (easy to go back and look):

“Skeptics” now arrive and claim to “debunk” the science of the IPCC by debunking Al Gore’s movie. They rely on the ignorance of their audience. Or demonstrate their own.

See how it’s different from what you claimed I wrote. You said I claimed that “those who disagree with the causation part ‘rely on the ignorance of their audience..’ ”

For other readers who are confused just go back and re-read my conclusion and see what I really said.

It seems from this discussion of ice core data that the complexity of climate is such that even complicated scientific analysis is in comparison little more than informed speculation, the direction of which is established as much by the Author’s personal agenda/ group think as from the analysis.

I have just come across your site and appreciate your analysis. I am a reasoned skeptic, that started out accepting the AGW position until I got deep into the reports and blogs on both sides. I agree, and think most serious skeptics agree, there has been some climate variation which has led to recent warming, and that CO2 and methane have some effect on warming. However, without positive feedback, the increase is known to be only modest, and almost surely not dangerous. In fact, the increased CO2 as plant food and slightly warmer temperatures are all positive factors. What we are skeptical about is the extreme positions (Hansen, Gore, and the IPCC recent positions). I would ask you to state your position on positive feedback, and if you accept the extreme positions. While a point can be made that it is a precaution to worry about warming (rising sea level, storms, drought, dangerous heating), I am more worried about cooling (new LIA, crop failure, freezing, glaciers forming), and in fact the evidence is strong that we are approaching the back end of the present interglacial. In addition, many scientists now predict the next 20 years to be a cooling period.

However, new evidence has recently demonstrated that water vapor is acting as a positive feedback. This study by Dessler (2009) showed that relative humidity stayed constant when averaged across the globe and the 10 years of measurement. If relative humidity is constant then as temperatures rise, we will have more water vapor. And water vapor is a strong greenhouse gas. This would be quite a simple positive feedback – and not requiring complex climate models to predict.

Still this evidence is quite new. Others might find different results.

I’m not yet sure what to think about positive feedbacks, or about the ability of Global Climate Models (GCMs) to predict/project the future.

I’d also be very skeptical of the scientists predictions of the coming cooling period. How did they predict it?

To return to your main point (which wasn’t the subject of the post! but of course it is the hot topic) – there are a number of positive feedbacks in the climate system, and you can see this demonstrated in the past history of climate.

If there were only negative feedbacks in the climate system there wouldn’t be the big changes in temperature that we have seen in the past million years.

Ice albedo, CO2 out-gassed from the ocean and water vapor probably provide positive feedback. Putting a number on the outcome seems “over-confident”.

Other factors are like jokers in the deck. Watch out for the post on the thermohaline currents, hopefully with a more exciting name.

This site has a healthy back-to-basics approach to CO2 and it’s effects. However, I thought the reply to James Gardiner comes across as defensive. While you have not said or supported it, the role of CO2 in the ice ages has been severely oversold to the public. Today, there is still an annoying rearguard action through the claimed amplification. While it may be there, I have not been able to locate anything conclusive. To the contrary, detailed calculations of the out gassing of the oceans after a significant temperature increase seem to match quite well with the observed CO2 trajectory.

I am not trying to deny the convective and radiative balance of the clear atmosphere. However, I do consider the possibility of negative cloud feedback from the slight change in temperature profile made by CO2 doubling. After all, we are trying to draw conclusions about climate from a very short interval with a poor signal to noise ratio.

Note that a strong negative cloud feedback would probably occur for other warming periods too, thus limiting the temperature rise. Large variations have been observed, and with strong negative feedbacks, the initial forcings should have been extremely large.

Note that you would somehow have to increase low level cloudiness, and that it is not at all clear that this happens of will happen from heating the atmosphere by CO2. There will be more moisture available for clouds to form, but you would need to increase the lapse rate for that moisture to actually condense.

Probably much too simply put, I would expect increases in solar irradiance to heat the surface, which would lead to increasing evaporation and a greater lapse rate near the surface and cloud formation (until the lapse rate very rapidly stabilizes again at a higher temperature and water content), but increases in GH forcing also heat the atmosphere, so it’s effect on the lapse rate is much more difficult to understand. Any feedback that reaches equilibrium shortly after the initial forcing perturbation can not amplify the forcing much.

Not sure I follow your argument. The lapse rate is a function of relative humidity. The relative humidity is not expected to change much in the troposphere.

I have been studying the following article in my quest to understand the subtleties of the atmosphere that we need to understand to draw conclusions. I thought you might find it of interest. Caution, not an easy read:

I have a few thoughts which I think are related to this particular post.

First, the rate of CO2 increase/decrease in the ice-core record would seem to be very different in its rate of change over the past 150 years. You might call it “d[CO2]/dt”. Those ice-core graphs tend to be very compressed time-wise. Plotting a portion of even one of the steeper increases in the ice-core record on the same time scale as modern CO2 and temperature increase would seem to me to be indicative of very dissimilar processes. Is there a simple conclusion we could draw from rates of carbon increase/decrease (and temperature increase/decrease?).

Second, (this one may be off-topic but I’ll throw it out anyway). Do the ice-core data tell us anything about CO2 residence times. I’ve heard conflicting claims about CO2 residence time in the atmosphere. Some say it would take hundreds of years for CO2 concentrations to fall back to (say) 350 ppm after cessation of emissions. Others (Freeman Dyson, I think) say that it is much shorter (and I think they draw their conclusions from analysis of the heights of the waves in the Keeling curve).

I have seen on a couple of sites now people discussing “co2 follows temp” and generally most people can understand the idea that extra warmth from solar or orbital changes can in theory warm the oceans and permafrost etc to cause a release of co2. But when it comes to the opposite scenario of a cooling world absorbing co2 back into the oceans and resulting in a positive feed back in both directions some people just can’t see that it would be possible. To me it seems perfectly simple in either direction if it is just remembered that the changes in temp and co2 are happening at a glacial pace compared to today and so the climate would always be very close to equilibrium. Changes of co2 going into and coming out of glaciations were in the order of 1.5-2 ppm per century and so there would never be much potential warming waiting in the pipeline such as we have now and it would only require a small change in orbital or solar forceing to set the ball rolling in the other direction.
Congratulations on a fantastic blog.

There is little downside to the “threat” of additional CO2 in the atmosphere. Isn’t there a balance between the use of CO2 by plants, making plants more efficient in their use of nutrients and using less water, thus vegetating more marginal steppe regions. The conversly creating more O2?

The fact that temperture increases prior to CO2 rise only indicates that CO2 may be released naturally from “locked up” organic material. I don’t want to seem “cosmic” in my statement, but may be natural as the process to “recover” from “ice ages” might suggest “natures way” to provide aerial fertilizer to “jump start” Vegetation growth and enhance the recovery from the ice age.

Just curious as to “varibility” around this number and how well the physics back this up? e.g. is the number likely to be between 1.1C and 1.3C or 0C and 2C or 0C and 10C etc.

Also is this number a “widely” agreed value.

Just to clarify, I had said, in answer to another commenter:

You are right when you say that without positive feedback the increase is modest.

The approximate increase in the earth’s global mean surface temperature from a doubling of CO2 (from pre-industrial levels) would be about 1.2′C.

The key point is – without feedbacks. As it is well-understood physics the uncertainty is low. But of course, there will be feedbacks and this is the difficult part about climate science. However, without first establishing the basics we cannot move forward.

SOD: You are outraged at the behavior of John Coleman: “So the creator of this “documentary” hasn’t even bothered to check the IPCC report. They agree with him. And even more amazing, they put it in print!” Do you have any comments on the behavior Al Gore and his scientific advisors who (with far greater resources) have spread misconceptions about climate science? They put it in a movie they are trying to distribute to every school in the world! If the IPCC really wanted the public to understand the role of CO2 in ice ages, they would put the information in the SPM, not bury it on p203 of a multi-thousand page report. The content of the SPM is controlled by political leaders, so this is unlikely to happen.

May I revert to the original topic of this post: “CO2 Lags Temperature in the Ice-Core Record. Doesn’t that prove the IPCC wrong?”.
IPCC may be wrong about a lot of things. However what the aforementioned lag tells us is that during glacial-interglacial (and v.v.) transitions changes (‘forcings’ in the jargon) in global atmospheric concentration of CO2 were not a driving force in local temperature changes at the Vostok site. CO2 may still have acted as a positive
feedback. However as far as I am aware the Vostok record taken in isolation provides no evidence regarding the size (or the existence) of such a feedback effect. But it does not rule out the possibility of a CO2 feedback operating during the glacial transitions, nor the possibility that recent anthropogenic increases in atmospheric CO2 content have caused earth’s surface temperatures to be higher than they would otherwise have been.
So to that limited extent the answer to the above question
seems to be ‘No’.

There’s something fundamental missing from both this page and the corresponding pages at Skeptical Science — a simple statement to point out an obvious fact that is overlooked by many of the anti-AGW arguments that refer to paleoclimate:

==> One big difference between the Earth’s circumstances now, and its circumstances at any time before the Industrial Revolution, is:

We now have billions of manmade machines emitting carbon dioxide. <==

Never before in the history of Earth has there existed this anthropogenic source of carbon dioxide increase that doesn't depend on ocean outgassing or any other natural source of carbon dioxide.

Volcanoes also emit CO2, but recently at less than 1% of the current anthropogenic rate. So, while volcanoes could have caused CO2-led temperature increases at some times, such as Snowball Earth episodes, the current CO2 increase cannot be explained by natural sources. Especially huge volcanic outbursts in the past might have emitted CO2 at rates comparable to, or dwarfing, current anthropogenic rates, but those have been rare and do not apply today.

Might you be overlooking the point that in light of the fact that for the last million years the Earth has been locked into a clockwork cycle of ice ages wherein the avg global temp is 8 degr C lower than at present, and that this cold part represents 90% of the cycle time? And that we are near the end of our present 10% comfy break from the cold? We had better hope our machines CO2 exhaust are producing a forcing!

In both papers it is found not only that CO2 lags temperature, but also that the role of CO2 is secondary.

Richard Lindzen mentioned the first paper in “Climate science: is it currently designed to answer questions?” (2008).

The same paper was discussed a few days ago at Lubos Motl’s blog. Motl points out that the Roe correction explains most of the NH 100,000 year temperature signal and leaves little for amplification by CO2 to account for.

I found the second paper by looking at papers citing Roe 2006. I noticed that Toggweiler has found much the same in the SH – only a secondary role for CO2 in explaining hemispheric temperature variations.

Although these are newer papers, newer theories, they seem to have been accepted by the community – or at least I can’t find papers refuting them. So don’t these results contradict the standard explanation that small Milankovitch forcings amplified by the large CO2 forcing explain the 100,000 year temperature variations?

A while back, after reading 20+ papers on the theories of the ice ages including the paper you cited from Roe I found that I couldn’t:

a) make sense of the different theories
b) see clearly enough to write about the confusion between, or coherence of, the different theories

There appear to be many different theories going under the name of Milankovitch. There appear to be problems with finding a climate mechanism to explain how the small change in solar insolation at a particular latitude and time of year creates such a large change in climate.

The theory that might be produced to explain the plunge into an ice age usually has problems explaining the return to an inter-glacial.

As you mentioned Lubos Motl I had a look at his article. Motl notes the beautiful match between theory and data, but I’m not sure the results are so amazing. Or at any rate, more amazing than all of the other theories that have beautiful matches in certain areas.

The top graph is a record which is “tuned” by the Milankovitch cycles (because dating has some uncertainty). So the results which match the theory so well were partly generated by assuming the theory..

The bottom graph is a more reliable assessment. Here is a zoom in on the last 200,000 years:

Note that black is the rate of change of ice volume and green is the insolation at 65’N.

To get the theory to work we have to assume that the dating of some of the the most recent changes (last 100,000 years) in ice volume is wrong. (Because the change in ice volume precedes the solar forcing change). Or that other effects are just as significant.

All of which makes it tricky.

Still, all of this rethinking makes me want to take another longer look and finally write a useful article.

I note that studies that infer climate sensitivity from ice core data (e.g. Hansen et al. 1993, which looks at the last glacial maximum (LGM)) simply assume that equilibrium climate sensitivity (lamba) can be obtained from the equation, delta_T = lamba * delta_Q and that the change in total forcing (delta_Q) and change in temperature (delta_T) are quantities known from the ice core data. They write:

“Based on knowledge of conditions during the last major ice age…, we know the alterations on the Earth’s surface and in the atmosphere that maintained the lower temperature, regardless of what caused the climate change. These were: increased reflection of sunlight by the continents, due to ice sheet growth and vegetation changes, decreased greenhouse gases CO2, CH4, and N2O, and increased atmospheric aerosol particles, which scatter sunlight to space. These surface and atmospheric changes caused a total forcing of 7.1 +/- 1.5 W m-2 ….”

The argument seems to be circular in that there is an unstated assumption that only the globally and annually averaged radiative forcing can in principle cause climate change (Lindzen 1993).

Thus, the Roe paper is cited in Hansen et al. 2007 (Climate change and trace gases, Phil. Trans. R. Soc. A 365, 1925–1954 doi:10.1098/rsta.2007.2052), and Hansen appears to accept Roe’s result, yet at the same time sees no problem for his earlier climate sensitivity estimate.

Richard Lindzen seems to be the only person who has ever disputed the idea that radiative forcing is the only that can cause climate change (e.g. Lindzen 1993: Paleoclimate sensitivity. Nature, 363, 25-26; Lindzen and Pan 1994: A note on orbital control of equator-pole heat fluxes. Clim. Dyn., 10, 49-57). I find it odd that there haven’t been more scientists disputing this apparently very simplistic approach to climate sensitivity.

Anyhow, I will look forward to your future post, should you get around to writing it.

The rate of change in ice volume is reasonably well explained by Milankovitch forcing except during glacial/interglacial transitions. Then the ice volume change is much larger than the radiative flux change at 65N. Not coincidentally, the CO2 level only changes significantly during glacial/interglacial transitions. I doubt very many serious scientists in the field think that CO2 is the primary cause of glacial/interglacial transitions.

In any case, the standard explanation is (quoting the Skeptical Science website),

“As the Southern Ocean warms, the solubility of CO2 in water falls (Martin 2005). This causes the oceans to give up more CO2, emitting it into the atmosphere. The exact mechanism of how the deep ocean gives up its CO2 is not fully understood but believed to be related to vertical ocean mixing (Toggweiler 1999). The process takes around 800 to 1000 years, so CO2 levels are observed to rise around 1000 years after the initial warming (Monnin 2001, Mudelsee 2001).

The outgassing of CO2 from the ocean has several effects. The increased CO2 in the atmosphere amplifies the original warming. The relatively weak forcing from Milankovitch cycles is insufficient to cause the dramatic temperature change taking our climate out of an ice age (this period is called a deglaciation). However, the amplifying effect of CO2 is consistent with the observed warming.”

So CO2 may not be “the primary cause of glacial/interglacial transitions” but it does appear to be the primary cause of the “dramatic temperature change” in the glacial/interglacial transitions – in the standard explanation.

The exact mechanism of how the deep ocean gives up its CO2 is not fully understood but believed to be related to vertical ocean mixing (Toggweiler 1999).

Indeed. The volume of CO2 released exceeds the change in solubility from the change in surface temperature. I did a crude analysis ( http://noconsensus.wordpress.com/2009/06/18/explaining-ice-core-co2-lag/ ) that suggests the time constant is more like 2,000 years than 1,000. That still produces what looks like an 800 year lag. If the time constant is too short, you get a too big a draw down during the Younger Dryas period than is reflected in the ice core record.
It looks somewhat like CO2 gradually accumulates somewhere in the deep ocean during a glacial cycle and it needs about 100,000 years after an interglacial period to reach a level where it can be discharged rapidly by an appropriately large Milankovitch excursion and help produce another interglacial period.

I decided to write to Dr. Roe for his opinion on the possible impact to understandings of climate sensitivity his 2006 paper might have. He gave me permission to reproduce his response at Lubos Motl’s blog.

In a few words, Dr. Roe appears convinced that his theory is right, and that it is accepted by others, but he does not seem to believe that it tells us anything about climate sensitivity.